1. Field of the Invention
The present invention relates to a fuel cell stack comprising a stack body formed by stacking a plurality of unit cells in a horizontal direction, and a casing containing the stack body. Each of the unit cells is formed by sandwiching an electrolyte electrode assembly between separators. The electrolyte electrode assembly includes a pair of electrodes and an electrolyte interposed between the electrodes.
2. Description of the Related Art
For example, a solid polymer electrolyte fuel cell employs an electrolyte membrane (electrolyte). The electrolyte membrane is a polymer ion exchange membrane. The electrolyte membrane is interposed between an anode and a cathode to form a membrane electrode assembly (MEA). The membrane electrode assembly and separators sandwiching the membrane electrode assembly make up a unit cell for generating electricity. In use, typically, a predetermined number (e.g., several tens to hundreds) of unit cells are stacked together to form a fuel cell stack for achieving the desired level of power generation output.
The fuel cell stack has the stack body formed by stacking a predetermined number of unit cells and a box-shaped casing containing the stack body. In order to suppress the increase in the weight and dimensions of the entire fuel cell stack, in most cases, the casing is made of thin metal plates. Under the circumstances, the stack body formed by stacking a large number of unit cells is considerably heavy. Therefore, since an excessively large load of the stack body is applied to the bottom of the casing, the bottom of the casing may be deformed undesirably.
In this regard, as shown in FIG. 17, a fuel cell disclosed in Japanese Laid-Open Patent Publication No. 08-171926 includes a lower case 1, and the lower case 1 is made up of a bottom part 2 and side parts 3. The bottom part 2 has an upwardly protruding curved portion 4, and curved portions 5 adjacent to the respective side parts 3.
Further, a downwardly protruding curved portion 6 is formed at the bottom part 2. The curved portions 4, 5 are used for positioning components stacked into a stack body (not shown). Moreover, the curved portions 4, 5, 6 achieve improvement in the rigidity of the lower case 1.
In the conventional technique, in particular, when the heavy stack body is disposed in the lower case 1, a considerably large load is applied to the bottom part 2. In particular, an excessively large load tends to be applied to the curved portion 4. Therefore, the bottom part 2 tends to be deformed easily in a direction to open the curved portion 4 (toward the side plates 3).